FIGS. 9a and 9b illustrate plan views of a conventional multiple volumetric feeder, and FIGS. 8a and 8b illustrate side views of this multiple volumetric feeder to which a raw-material-supplying hopper 95 is fitted. Conventional multiple volumetric feeders include those of reciprocating-type and those of rotating-type, as shown in FIGS. 9a and 9b and FIGS. 8a and 8b, respectively. The volumetric feeders shown in FIGS. 8a to 9b are furnished with a stationary portion 91, a movable volumetric measure 92 capable of moving back and forth in the stationary portion 91, and the movable volumetric measure 92 is furnished with a plurality of measure portions 93 for accommodating a predetermined volume of powdery or granular material. The stationary portion 91 is provided with a plurality of charging apertures 94 for supplying a powdery or granular material to the measure portions 93, and a plurality of discharging apertures 96 for discharging the powdery or granular material from the measure portions 93. In the multiple volumetric feeder thus configured, the powdery or granular material is supplied to all the measure portions 93 from the charging apertures 94 when the movable volumetric measure 92 is positioned on a raw-material-supplying hopper 95 side as shown in FIGS. 8a and 9a, whereas when the movable volumetric measure 92 is positioned on the far side from the raw-material-supplying hopper 95 as shown in FIGS. 8b and 9b, the powdery or granular material is discharged from all the measure portions 93 through the discharging apertures 96. This type of configuration, in which the powdery or granular material is simultaneously discharged from all the measure portions 93, is common to both the reciprocating-type and the rotating-type, and the function to supply the powdery or granular material only from a specific feeder is not provided.
In addition, in the conventional volumetric feeders, volume adjusting is performed for the purpose of making weights uniform, and based on the measurement results of the weight of the raw material discharged from a volumetric feeder, the weight of the raw material that goes into the measures of the volumetric feeder is manually changed by, for example, a gate 97 or the like as shown in FIG. 10.
In using such a conventional volumetric feeder for a powdery- or granular-material combination weigher, the number of the scale units used for a combination to obtain a target weight is usually 4 to 5, for example, in the case where the powdery- or granular-material combination weigher comprises 12 scale units, and the weighing hoppers of the scale units used for the combination are emptied and therefore must be resupplied with the powdery or granular material. However, since the weighing hoppers that have not been used for the combination must not be supplied with the powdery or granular material, the above-described conventional multiple volumetric feeders as they are cannot be employed for a powdery- or granular-material combination weigher, and a mechanism is required that is capable of supplying the raw material only to desired heads.
Then, the average value of the weights that are charged to the weighing hoppers of the scale units is represented as (target weight)/(number of scale units to be combined). If, for example, the weight of the powdery or granular material in each of the scale units results in a weight less than the above-described average value, an appropriate combination cannot be obtained. For a specific example, assuming that the targeted combination weight is 100 g and the number of scale units to be combined is 4, the average weight of the powdery or granular material to be charged into the weighing hopper of each of the scale units is 25 g. If, however, the weights of the powdery or granular material in the weighing hoppers become uniform at about 23 g in a condition that does not permit a weight less than a specified weight, the weight that is closest to the target will be 23 g×5=115 g, producing a margin of error of as large as 15 g. For this reason, in a combination weighing system, it is necessary to impart appropriate variations to the weights of the powdery or granular material in the scale units.
The present invention has been accomplished to solve such problems in the prior art. It is an object of the present invention to provide a volumetric feeder that can be used for a powdery- or granular-material combination weigher, and it is another object of the present invention to provide a powdery- or granular-material combination weigher that uses such a volumetric feeder.